1. Field of the Invention
The present invention relates generally to magnetic tape cassettes and more particularly is directed to a magnetic tape cassette suitable for use in a recording/reproducing apparatus for recording digital signals, for example pulse code modulated signals.
2. Description of the Prior Art
Magnetic recording/reproducing apparatus for recording signals on and reproducing signals from magnetic tape are well known in the art. In such apparatus, an analog signal, such as an audio signal, is converted into a digital signal, which may be a pulse code modulated (PCM) signal, and then recorded at a high density on a magnetic tape contained in a cassette by means of a rotary magnetic head. Upon a recording or reproducing operation, the magnetic tape is withdrawn from the cassette and wound around the periphery of a rotary drum within which the rotary head is provided. An opening at the front of the cassette is provided for permitting withdrawal of the tape from the cassette.
In addition, the tape is wound about two reel hubs within the cassette, which receive drive shafts of the recording/reproducing apparatus when the cassette is inserted therein for winding or rewinding the tape. In order to permit the reel shafts to be inserted into the reel hubs, the cassette has insertion apertures which receive the reel hubs with a small degree of clearance, so that the hubs may be smoothly rotated.
It is very important in such a cassette that the magnetic tape be protected from contamination by oil or dust. If the tape is contaminated, the signal cannot properly be reproduced and a drop-out in the reproduced signal occurs, leading to reduced quality in the reproduced audio signal. Therefore, to prevent such contamination, as from fingerprints or dust and pollution in the atmosphere, the magnetic surface of the tape should ideally be maintained sealed within the cassette. However, the front opening and apertures described above constitute openings through which dust and unwary fingers may enter to damage the tape.
In order to close the front opening in a cassette of this type, there has been proposed a cassette with a pivotable front lid which covers the front of the cassette. This rotatable front lid can cover either the front surface or the magnetic surface of the magnetic tape, and an opening is provided in the front lid for inserting therethrough a tape guide system for withdrawing the magnetic tape from the tape cassette.
However, with this proposed tape cassette, it is still possible for the magnetic tape to be touched or contaminated through the space through which the tape guide system is inserted. Moreover, although the magnetic surface of the tape is covered by the front lid, there is still a small clearance between the front lid and the magnetic surface of the tape, so that dust and contamination may still reach the magnetic surface of the tape and adhere thereto.
Therefore, it has been further proposed that an inner lid be provided inside the front lid to cover the tape surface opposed to the magnetic surface, so that the magnetic tape will be enclosed between the front lid and the inner lid. Although in such a tape cassette the magnetic tape is protected, this construction is relatively complicated and assembly thereof may be quite difficult.